Asthma

Published on 10/03/2015 by admin

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Chapter 21 Asthma

Ali Al-Alwan, MD , Gilman B. Allen, MD , David A. Kaminsky, MD

1 What are important factors to address when taking the history of patients with acute severe asthma?

Box 21-1 summarizes the important historical points in a patient with acute severe asthma. If the clinician is able to obtain a history from the patient, it is important to first exclude other possible causes of the patient’s presentation. A history of heart failure may suggest wheezing and shortness of breath resulting from left ventricular failure and pulmonary edema. A history of allergies or prior anaphylactic reactions, along with a recent exposure to certain foods, new medications, or other known triggers, could be an important warning of potentially imminent upper airway inflammation and closure. A history of recent-onset cough, wheezing, and hemoptysis with unilateral inspiratory and expiratory wheezes could be clues to an intrabronchial tumor, such as a carcinoid or carcinoma. Pulmonary embolism can also mimic asthma and should especially be considered in the patient with dyspnea, anxiety, and hypoxemia but clear breath sounds. In a patient with dyspnea, anxiety, and inspiratory stridor, vocal cord dysfunction should be considered. Spirometry can be an especially useful tool in the emergency department (ED) when evaluating these patients, and flow-volume loops often show the characteristic truncated or flattened inspiratory loops.

Box 21-1 Important Historical Points in Acute Asthma

History of asthma (i.e., when diagnosed, type of treatment, common triggers)

Timing of onset of symptoms (i.e., gradual versus sudden)

Nature of symptoms (e.g., wheezing, chest pain, intermittent versus continuous, associated cough, sputum production, fever)

Exclusion of other causes of shortness of breath (e.g., heart failure, pulmonary embolus)

Exclusion of other causes of wheezing (e.g., bronchospasm from allergic reaction, endobronchial tumor)

Consideration of paradoxical vocal cord closure on inspiration (i.e., vocal cord dysfunction)

3 Which patients are at greatest risk for near-fatal or fatal asthma?

A survey of North American adult patients with asthma seen in the ED identified a number of factors associated with a high number of ED visits, including nonwhite race, Medicaid, other public or no insurance, and markers of chronic asthma severity, such as history of prior hospitalization, intubation, or recent use of inhaled corticosteroids. Also at increased risk for near-fatal asthma are patients with a high degree of bronchial reactivity, those with a history of poor compliance with therapy and follow-up, and those judged to be poor at perceiving the severity of their own attack, as demonstrated by a poor correlation between reported symptoms and peak expiratory flow (PEF) values. These are patients for whom home monitoring of PEF is strongly indicated.

Patients in whom sudden, severe attacks develop or those who have severe, slowly progressive disease are both typically at risk. A history of marked diurnal variation in forced expiratory volume in 1 second (FEV₁) is also believed to be a risk factor, but this could simply be related to its being a marker for increased bronchial responsiveness. Historical data indicate that female sex, endotracheal intubation, and prolonged neuromuscular blockade are associated with more prolonged hospital stay, whereas elevated arterial CO₂ level and lower arterial pH within 24 hours of admission are associated with increased mortality.

Although not widely identified as a true marker of increased risk, the use of inhaled heroin is also frequently associated with near-fatal or fatal attacks of asthma. It is not known whether this is due to a direct effect of the inhaled drug (or its diluents), the degree of airflow limitation, or simply the impaired judgment of the user that delays arrival to the ED and initiation of appropriate care. However, opioids have long been known to cause bronchoconstriction via mast cell degranulation and histamine release. Although most reports of severe asthma attacks after inhalation of narcotics are in patients with known asthma, they have also been reported in patients without any history of asthma.

4 How should one treat a severe asthma attack?

Oxygen therapy to achieve an arterial oxygen saturation of 90% or greater.

β-Agonists: These are the first-line therapy in an acute asthma attack. It is now widely accepted that the inhaled forms of these drugs are superior to the subcutaneous or intravenous (IV) route, with fewer adverse affects, and their administration can be repeated up to three times within the first hour after presentation while monitoring for adverse effects such as tachyarrhythmia and lactic acidosis, the latter of which can be underrecognized. The subcutaneous route is still reserved for patients who have such severe dyspnea that they are unable to take deep-enough breaths, but these are usually the patients who later undergo intubation. It is also accepted that metered dose inhalers are as effective as aerosolized delivery, provided good technique is used with a spacer device. Nebulized or aerosolized delivery is still used frequently in the ED, in part from convention and in part because less instruction and observation are needed to ensure good delivery. The use of salmeterol as an outpatient monotherapy was recently shown to increase the risk of hospitalization. However, this increased risk was not seen among patients receiving combined therapy with inhaled corticosteroids and salmeterol (Table 21-1).

Corticosteroids: These drugs also play a key role in treatment, and typical dosage is 60 mg of IV or PO methylprednisolone every 12 to 24 hours for the first 24 hours. This must be delivered as soon as possible because peak onset of action can take several hours. Therapy is typically administered every 6 hours until the attack appears to be subsiding and then gradually tapered over days to weeks. Comparisons between oral prednisone and IV corticosteroids have not shown differences in the rate of improvement of lung function or in the length of the hospital stay. Thus the oral route is preferred for patients with normal mental status and without conditions expected to interfere with gastrointestinal absorption.

Anticholinergics: Many studies have shown a marginal benefit from adding inhaled ipratropium to β-agonist therapy (versus β-agonists alone) in the treatment of acute asthma.

Aminophylline: Oral theophylline is a third-line agent in the outpatient management of asthma. This is in part due to the recognition of its intrinsic antiinflammatory properties, even at serum levels lower than those once thought necessary to achieve significant benefit. However, the use of IV aminophylline in the treatment of acute asthma remains controversial and is no longer recommended.

Inhaled epinephrine: A recent meta-analysis of using inhaled epinephrine in refractory asthma demonstrated a similar degree of bronchodilation and PEF improvement when compared with albuterol. The use of inhaled epinephrine is safer than IV epinephrine, which is associated with a higher risk of acute myocardial infarction and tachyarrhythmias.

Inhaled anesthetic agents: In patients receiving mechanical ventilation with ongoing severe bronchospasm despite aggressive conventional treatment, inhaled anesthetic agents can be used for their intrinsic properties of bronchodilation. Because their delivery requires a special apparatus and conventional therapy is usually more effective, their use is often considered as a rescue therapy only. Isoflurane or enflurane are the agents of choice.

Antibiotics: There is no benefit to the routine use of antibiotics in the management of an acute asthma episode unless findings are suspicious for pneumonia or other bacterial infections.

^{Table 21-1} Primary Pharmacologic Treatment of Acute Asthma *

Agent	Dose	Comments
β-Agonists	4-8 puffs (90 mcg/puff) MDI + spacer, every 20 min up to 4 hr, then every 1-4 hr as needed or 2.5-5 mg nebulized every 20 min for 3 doses, then every 1-4 hr as needed